This application is a 35 USC 371 of PCT/JP99/04032 filed Jul. 28, 1999.
The present invention relates to a thin sheet metal member having a predetermined shape, and especially, a sheet metal member which is available as a partition of a gas generator of an air bag used for an automobile, and a method of manufacturing the same.
Conventionally, a thin disc-shaped blank having the substantial thickness of 0.4 to 1.2 mm has been used. There has never been a sheet metal member which is formed so as to comprise a circular base plate and an annular projection concentrically and integrally formed with one or both surfaces of the circular base plate, in a bulged state, and a processing technology thereof.
The present invention has an object to provide a sheet metal member which is formed so as to have a circular base plate and an annular projection integrally formed with one or both surfaces of the thin and circular base plate in a bulged state, so as to be concentric with each other, and a method of manufacturing the same.
Moreover, the present invention has another object to provide a sheet metal member having the above shape, which is lightweight and durable.
Furthermore, the present invention has still another object to provide a method of manufacturing a sheet metal member which is formed so as to have a circular base plate and an annular projection concentrically and integrally formed with one or both surfaces of the thin and circular base plate, in a bulged state, using minimum steps. The method thereof can achieve reduction of material without producing cutting waste, and make it easy to produce the sheet metal member economically.
According to the present invention, a sheet metal member, which is made from a thin disc-shaped blank, is characterized in that an annular projection is integrally formed with at least one surface of a circular base plate, so as to be concentric with each other, and said annular projection is formed by drawing an outer peripheral portion of the base plate so as to decrease a thickness of the outer peripheral portion of the base plate, and axially bulging it.
The sheet metal member having the above structure is lightweight and durable.
According to the present invention, a method of manufacturing a sheet metal member, which is made from a thin disc-shaped blank, wherein an annular projection is integrally formed with at least one surface of a circular base plate so as to be concentric with each other, comprises the steps of:
rotating the thin disc-shaped blank in a state of holding the thin disc-shaped blank between upper and lower dies, at the same time while pressing a groove on an outer peripheral surface of a thickening-forming roller, against an outer peripheral portion of the blank which extrudes outwardly from the upper and lower dies, thereby thickening the outer peripheral portion of the blank; and
rotating the blank which have a thickened outer peripheral portion in a state of holding it between another upper and lower dies, at the same time while pressing an edge angle portion of an outer peripheral surface of a drawing roller against one surface of the thickened outer peripheral portion which extrudes outwardly from the upper die of the blank, and rotating the drawing roller, and
drawing the thickened outer peripheral portion thereof so as to make it thin, while moving it in the direction of the center of the blank, thereby bulging the annular projection axially.
According to the above manufacturing method, the thin and circular blank is used, and it is subjected to rotation-drawing process by means of the drawing roller. As a result, the sheet metal member which has an annular projection concentrically and integrally formed with at least one surface of the circular base plate, can be easily and economically obtained by only a few steps, because cutting waste is never produced from the material.
The drawing roller draws one surface of the thickened outer peripheral portion at the edge angle by providing a clearance angle for providing a clearance so as to prevent a lower surface of the drawing roller opposed to the drawing surface of the thickened outer peripheral portion from abutting against the drawing surface.
This can prevent the lower surface of the drawing roller from being burnt on the drawing surface of the thickened outer peripheral portion. Furthermore, this makes it easy to perform the drawing process.